The present invention relates to systems for coupling a plurality of physiological signals across an isolation barrier.
Patient monitoring instruments commonly provide the capability of monitoring a multiplicity of physiological functions, for example, ECG, respiration, blood pressure, body temperature, etc. Isolated front end circuitry to which the monitoring electrodes are coupled serves to isolate the patient from sources of potentially dangerous electrical power. In one commonly used isolation technique, the primary winding of a transformer is connected to the front end circuitry to receive the input signals and transmit such signals to its secondary winding without providing an electrically conductive path between the front end circuitry and the remaining circuitry of the instrument. To reduce circuit complexity and cost, the input signals are time division multiplexed and then provided to the primary winding to be transmitted to the non-isolated circuitry.
To avoid unacceptably high levels of cross talk between the signals, it is necessary to provide a substantial dead time between signals to dissipate the residual magnetization of the transformer resulting from the signals previously transmitted. Accordingly, in a given system the data rate is limited by the need to introduce such dead time intervals between signals which has the effect of either limiting the number of signals which may be transmitted across the barrier and/or signal bandwidth.